when it has suggested fast pass, do you attempt to get the fast pass for the time they are recommending or as soon as you can?
I try to get it when it suggests, and if that doesn't work, I re-evaluate the plan.
As near as you can, but as long as the time it has you arriving at the ride on the plan is within your window, you're ok.
what is they don't recommend any
Look at your longest waits and try to book for those rides. Unless you're going on a CL 1 or 2 day though, it should recommend some. You need to tick the box to say how many you have though.